The present invention relates to a rod antenna favorable for use in a portable transmitting/receiving apparatus such as a portable telephone and a portable terminal.
FIGS. 4 and 5 show a constitution of a prior art rod antenna used in a portable transmitting/receiving apparatus. FIG. 4 is a vertically sectional side view of the whole of the rod antenna, while FIG. 5 is also a vertically sectional side view of only the antenna element thereof.
The rod antenna 20 is freely inserted into a case 31 of the portable transmitting/receiving apparatus 30 and drawn therefrom, as indicated by the arrows in FIG. 4. The rod antenna 20 is also electrically coupled to a feeder section 32, provided near to an antenna inserting/drawing hole 31a of the case 31, using a certain coupling means.
As illustrate in FIG. 5, the antenna element 21, which is the principal part of the rod antenna 20, is constituted by supporting first and second conductive lines 23a and 23b each having a predetermined length by three insulating columns 22a, 22b and 22c such that the conductive lines and insulating columns are arranged in a straight line and separately from each other and then covering them with an insulating tube 24.
Returning to FIG. 4, in the antenna element 21 so constituted, its outer surface except both end portions is covered with an armoring tube 25 of insulating material. A bottom portion of the antenna element 21 is coated with a bottom-portion protecting cylinder 26a formed of insulating material, while a top portion thereof is coated with a cap 26b formed of insulating material. The rod antenna 20 is thus completed as illustrated in FIG. 4.
The above-described prior art rod antenna 20 has the following drawback. In order to form the antenna element 21 of the rod antenna 20, the first and second conductive lines 23a and 23b have to be positioned with high precision such that the conductive lines and three insulating columns 22a, 22b and 22c are arranged concentrically in the straight line, and they have to be molded using insulating molding materials such as resin and covered with the insulating tube 24. Since, therefore, the antenna element 21 is complicated in structure and requires a large number of parts, it cannot be miniaturized or lightened, thus making it difficult to manufacture the rod antenna and increasing in costs therefor.